+1

internal/app/handlers/register.go

@@ -118,3 +118,4 @@ func (d *RegisterHandler) register(
 		Ok: true,
 	}, nil
 }
+

internal/common/request.go

@@ -48,8 +48,11 @@ type Request struct {
 	ID      string
 	Session *models.Session
 	User    *models.User
+	// ResolveValues - data required to process request.
 	ResolveValues *sync.Map
+	// Metadata - an additional data, usually added with preprocessing.
 	Metadata *sync.Map
+	// Request body
 	Body   []byte
 	RawReq *http.Request
 }

internal/handler/handler.go

@@ -15,12 +15,14 @@ type Handler interface {
 	GetName() string
 	GetRequiredResolveParams() []string
 	GetProcessFn() func(ctx context.Context, req *common.Request, w Writer) error
+	GetPreprocessFn() func(ctx context.Context, req *common.Request, w Writer) error
 }
 
 type BaseHandler struct {
 	Name                  string
 	RequiredResolveParams []string
 	ProcessFn             func(ctx context.Context, req *common.Request, w Writer) error
+	PreprocessFn          func(ctx context.Context, req *common.Request, w Writer) error
 }
 
 func New() *BaseHandler {
@@ -42,6 +44,11 @@ func (h *BaseHandler) WithProcessFunc(fn func(ctx context.Context, req *common.R
 	return h
 }
 
+func (h *BaseHandler) WithPreprocessFunc(fn func(ctx context.Context, req *common.Request, w Writer) error) *BaseHandler {
+	h.PreprocessFn = fn
+	return h
+}
+
 func (h *BaseHandler) GetName() string {
 	return h.Name
 }
@@ -53,3 +60,7 @@ func (h *BaseHandler) GetRequiredResolveParams() []string {
 func (h *BaseHandler) GetProcessFn() func(ctx context.Context, req *common.Request, w Writer) error {
 	return h.ProcessFn
 }
+
+func (h *BaseHandler) GetPreprocessFn() func(ctx context.Context, req *common.Request, w Writer) error {
+	return h.PreprocessFn
+}

internal/processor/gin_processor.go

@@ -47,8 +47,12 @@ func (p *GinProcessor) Process(handler handler.Handler) gin.HandlerFunc {
 			return
 		}
 
-		// 3. Call preprocessinf fn's, middlewares etc.
+		// 3. Call preprocessing fn's, middlewares etc.
-		// ....
+		if err = handler.GetPreprocessFn()(ctx, req, wrapGin(ctx)); err != nil {
+			p.writeError(ctx, err)
+			return
+		}
+
 		// 4. Call handler.ProcessFn
 		if err = handler.GetProcessFn()(ctx, req, wrapGin(ctx)); err != nil {
 			p.writeError(ctx, err)